Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C3/00—Selection of compositions for coating the surfaces of moulds, cores, or patterns
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/02—Sand moulds or like moulds for shaped castings
  • B22C9/04—Use of lost patterns

Definitions

• the present invention pertains to a method of protecting castings made of carbon-containing alloys against decarburization at the edges thereof and against the formation of surface defects during cooling in a mold which is fired prior to casting.
• Molds of this type are much used in the manufacture of precision castings. These molds are formed about a model or pattern of the piece to be cast, which pattern is melted, dissolved or otherwise destructively removed from the mold formed about it.
• the edge regions of the castings may under certain circumstances decarburize to an undesirable degree during cooling.
• surface defects often appear, especially in the form of pittings. Such phenomena are particularly noticeable when the melt is poured into the mold while the mold is hot, as is customary in precision casting operations, the molds being in such cases removed from the furnaces in which they are fired immediately prior to the casting operation itself.
• the invention provides a great and striking improvement in the protective effect achieved.
• a protective material whose melting point is below that at which the casting is poured but which lies above the firing temperature of the mold, which firing temperature is at least 800 C.
• the increased protective effect of the material employed in accordance with the invention rests upon the fact that its susceptibility to reaction, after it has been liquefied by the heat of the melt, is much larger than that of known protective agents which are in the solid state in the mold when they develop their protective action.
• the protective material preferably comprises a silicide or a mixture of silicides. Particularly good results have been obtained with calcium silicide whose melting point is in the range from about 920 C. to 1220 C. Alloys of aluminum and silicon, especially those having a content of at least 30 percent aluminimum and 20 percent silicon, are other good protective materials for use in the invention.
• EXAMPLE 1 250 kilograms of finely ground fire clay, 25 kilograms of refractory cement, and 25 kilograms of CaSi are mixed with Water to form a slurry-like mold material.
• a wax pattern of the piece to be cast, coated in known fashion with a refractory overlay of granular zirconium and aqueous colloidal silicic acid is positioned in a flask and the flask is filled with the mold material around the pattern.
• the mold so obtained is fired overnight at a temperature of about some 900 C., in the course of which firing the wax pattern is destroyed.
• liquid 13 percent chromium steel at a temperature of about 1600 C. is poured into the mold.
• the melting point of the calcium silicide in the mold is in the vicinity of 1220 C. so that it will have remained in the solid state during the firing of the mold, in which state it is relatively inert in the face of the oxygen present in the atmosphere of the firing furnace. It is consequently unnecessary to maintain a reducing or inert atmosphere in that furnace.
• the composition of the steel used in this example was, in weight percents:
• the finished casting is characterized by a uniform distribution of carbon therein, including the surface layers thereof, and it exhibits an excellent surface quality substantially free from surface pitting.
• CaSi calcium silicides
• Ca Si having a fusion point of 920 C.
• CaSiO having a fusion point of 1020 C.
• Good results are obtained with from 2 to 15 and especially from 4 to 10 percent by weight of the protective material, taken by reference to the dry weight of the mixture from which the mold is made.
• EXAMPLE 2 A mold mixture is prepared from a solution of the liters of ethyl silicate, 2.5 liters of alcohol, 0.25 liter of water, 5 cubic centimeters of 32 percent hydrochloric acid and 18 kilograms of granular zirconium.
• a pattern of the piece to be cast made of urea is dipped into the mold mixture so produced and, after drying of the coating so obtained, this process is repeated.
• the surface is scattered over with a finely ground aluminum-silicon alloy to provide a protective material.
• This aluminum alloy comprises about 0.8 percent carbon, 33 percent silicon, 48 percent aluminum, 3 percent titanium, 13 percent iron and the usual accompanying elements and impurities and is commercially available under the name Alsimin.
• This powdering of the surface is repeated after the fifth, sixth, seventh and eighth dippings, the eighth dipping being the next to last.
• the quantitiy of protective material so incorporated amounts to about 14 percent by weight of the dry weight of the material in the finished shell-like mold thus obtained.
• the shell-type mold thus obtained is allowed to dry and solidify for several hours in air and is then immersed in water which dissolves out the urea pattern at the core. This dissolving can be allowed to proceed to completion or only part way, in which latter case the remainder will be removed upon firing of the mold. Firing is effected in a furnace for 6 hours at a temperature of 900 C. The protective material existing between the dipped layers maintains its solid condition during the firing since its melting temperature is about 1100 C.
• the mold After removal from the furnace, the mold is poured with a carbon-containing steel having a melting temperature of 1600 C. Under the influence of the heat in the melt, the aluminum-silicon alloy fuses and is effective as a protective against edge decarburization. Preferable reducing elements are aluminum, silicon and titanium. The piece so cast is free of all edge decarburization and shows a very good surface quality.
• the invention is not limited to the example described. Other methods may be employed for production of the mold such as those in which the pattern, without any dip-formed coatings thereon, is packed in a mold flask with a mold material having the protective substance uniformly distributed through it.
• the invention thus provides a method of protecting castings of carbon-containing alloys against decarburization and the formation of surface defects during cooling in a previously fired mold.
• a material which is capable of combining with oxygen when, during cooling of the melt, that material is heated to a temperature above that at which the mold is fired, the material having a melting temperature above 800 C. and above the temperature at which the mold is fired, but below the temperature at which the melt is poured.
• the inventin provides a process of casting carbon-containing alloys according to which there is made a mold including a material having a melting temperature above 800 C. and having an afiinity for oxygen when heated above its melting temperature. Further according to this process of casting, the mold is fired at a temperature of at least 800 C. but below the melting temperature of that material, and there is poured into the mold a molten carbon-containing alloy heated to a temperature above that melting temperature.
• a process of protecting castings of carbon-containing alloys against decarburization and the formation of surface defects during cooling in a mold comprising making a porous mold and including in the body thereof a solid protective reducing material having a relatively low afiinity for oxygen when said material is in its solid state, said material becoming liquefied at temperatures considerably above 800 C. and having when liquefied a relatively great afiinity for oxygen, said material comprising a mixture of silicides, CaSi, Ca Si and CaSiO and choosing a mixture thereof to vary the fusion point of said protective material, firing said mold before casting to a temperature of at least 800 C. and introducing a melt into said mold having a temperature considerably above 800 C., said protective material becoming liquefied in the temperature interval between the temperature at which the melt is poured and the temperature of at least 800 C. at which the mold is fired.
• a process of protecting castings of carbon-containing alloys against a decarburization and the formation of surface defects during cooling in a mold comprising making a porous mold and including in the body thereof a solid protective reducing material having a relatively low afiinity for oxygen when said material is in its solid state, said material becoming liquefied at temperatures considerably above 800 C. and having when liquefied a relatively great affinity for oxygen, said material comprising an aluminum-silicon alloy wherein the aluminum content comprises at least 30%, firing said mold before casting to a temperature of at least 800 C. and introducing a melt into said mold having a temperature considerably above 800 C., said protective material becoming liquefied in the temperature interval between the temperature at which the melt is poured and the temperature of at least 800 C. at which the mold is fired.
• a process according to claim 2 wherein said alloy includes by weight at least 30% aluminum and 20% silicon.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)

Applications Claiming Priority (1)

Publications (1)

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Country Status (5)

Cited By (3)

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Citations (4)

Family Cites Families (5)

• 0
  • NL NL126286D patent/NL126286C/xx active
• 1965
  • 1965-07-29 CH CH1069765A patent/CH426112A/de unknown
  • 1965-07-31 DE DEP1271A patent/DE1271909B/de active Pending
  • 1965-09-10 NL NL6511828A patent/NL6511828A/xx unknown
• 1966
  • 1966-05-24 US US552426A patent/US3470937A/en not_active Expired - Lifetime
  • 1966-07-11 GB GB31054/66A patent/GB1149943A/en not_active Expired

Patent Citations (4)

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